1. Field of the Invention
This invention is directed to a process for preparing acrylonitrile using novel compounds containing critical amounts of uranium, antimony and an element from Group IV B of the Periodic Table.
2. Description of the Prior Art
Oxidation catalysts consisting essentially of oxides of antimony and uranium are old and well known. Such catalysts and their uses are described in U.S. pat. Nos. 3,198,750 and3,308,151 to Callahan and Gertisser. Antimony-uranium oxide catalysts are used primarily for converting propylene, in the presence of ammonia and a gas containing molecular oxygen, to acrylonitrile. Other uses include the ammoxidation of isobutylene to methacrylonitrile and the oxidative conversions of propylene to acrolein, isobutylene to methacrolein, butene-1 or butene-2 to 1,3-butadiene, and isoamylenes to isoprene. It has been shown by Grasselli and Callahan in the Journal of Catalysis, 14, 93-103 (1969) that the most effective catalysts are obtained when the antimony to uranium atomic ratio is greater than three. Their best catalyst had an antimony to uranium atomic ratio of 4.6. The sole uranium containing phase detected in this catalyst was USb.sub.3 O.sub.10 according to Grasselli and Suresh, Journal of Catalysis, 25, 273-291 (1972). The excess antimony oxide insured that undesirable uranium-containing phases, such as USbO.sub.5 and U.sub.3 O.sub.8 were not formed. U.S. Pat. No. 3,816,596 to Wise describes a method of making a catalyst consisting essentially of USb.sub.3 O.sub.10. Antimony-uranium oxide catalysts may be made attrition resistant by adding silica as described in U.S. Pat. No. 3,341,471 to Callahan et al.
Attempts have been made to improve the antimony-uranium oxide catalyst by combining the optimum antimony-uranium oxide composition with the oxides of most of the metallic elements of the Periodic Table. See, for example, U.S. Pat. Nos. 3,328,315 and 3,431,292 to Callahan et al and British Pat. No. 1,007,929 to Distiller's Company Limited. Based on starting materials, every catalyst tested in these patents had an antimony to uranium atomic ratio of 4.0 or 4.6, i.e. close to the optimum composition of Grasselli and Callahan.